Scar
One of the few surviving Ishbalans. His real name is never known, but he is referred to as "Scar" because of the X-shaped scar on his forehead. Scar's right arm, which is covered in an elaborate alchemical tattoo, was given to him by his brother shortly before he died. He believes himself to be an instrument of God, and kills State Alchemists by using alchemy to destroy their bodies from the inside, and can also use this power on inanimate objects as well.

Kenshin
Kenshin was a former Imperialist assassin that went by the name "Hitokiri Battōsai". The title implies he has mastered the technique of Battoujutsu (sword drawing technique, studied in modern times as Iaijutsu) and can draw his sword with lightning speed. Hitokiri was the title given to samurai assassins.

Even if I'm not a member of the Guild, I vote Kenshin. I haven't seen the episodes (unless you're counting one I saw in Japan), but I did read all the manga (in Japanese, too - what a pain in the ass.) About the only two manga I really ever liked were Rurouni Kenshin and DragonBall, and I don't really read the latter anymore.